The present invention relates generally to electrodes and methods for manufacturing the electrodes, and, more specifically, to electrodes applied in electro-machining processes and their manufacturing methods.
Electro-machining is a process for applying electric energy to a workpiece to effect removal of material, and it can be roughly divided into two categories based on the material removal process. The first category is electric discharge machining (EDM), in which thermal energy flows between a tool-electrode and the workpiece, causing material to be removed from the workpiece. The second category is electrochemical machining (ECM), in which an oxidation reaction occurs at the workpiece due to a chemical potential difference from the applied electric field and material is removed from the workpiece.
EDM is a manufacturing process whereby a desired shape is obtained using electrical discharges (sparks or thermal events). A tool and a workpiece, functioning as two electrodes, are separated by a dielectric liquid and subject to an electric voltage. The tool may be called the tool-electrode, or simply the “electrode”, while the workpiece may be called the workpiece-electrode. Material is removed from the workpiece by a series of rapidly recurring current discharges between the electrode and the workpiece.
When the distance between the electrode and the workpiece is reduced, the intensity of the electric field in the volume between the electrode and the workpiece (inter-electrode volume) becomes greater than the strength of the dielectric (at least in some point(s)), which breaks down, allowing current to flow between the electrode and the workpiece creating arc or spark discharges. As a result of the arc or spark an enormous amount of thermal energy is generated which melts a small quantity of material from both the electrode and the workpiece, and the melt is convected into the dielectric liquid, in which it is cooled to form solid particles or debris. After an electric discharge event the current flow stops, and new liquid dielectric is conveyed into the inter-electrode volume enabling the solid particles or debris to be carried away and the insulating properties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as flushing. Also, after a current flow, the potential difference between the electrode and the workpiece is restored to what it was before the breakdown, so that a subsequent liquid dielectric breakdown can occur.
ECM is a method of removing metal by an electrochemical reduction/oxidation process. It is similar in concept to EDM in that a potential gradient is applied between an electrode and a workpiece. Ions pass through an electrolytic material facilitating the removal process using a negatively charged electrode (cathode), a conductive fluid (electrolyte), and a conductive workpiece (anode). Contrary to EDM, in ECM no sparks are created and there is typically no electrode wear. In the ECM process, the electrode is advanced toward the workpiece but without touching the workpiece. The gap between the electrode and the workpiece may vary within 8-800 micrometers. The pressurized electrolyte is injected at a set temperature to the area being cut. As ions cross the gap, material from the workpiece is dissolved. The electrode is guided along the desired path to form the desired shape in the workpiece.
In addition, there is another technology utilizing thermal events to drive material removal, i.e., high speed electro-errosion (HSEE), which has been developed recently for machining difficult-to-machine, high-performance alloy workpieces. The HSEE process is applied to electrically conductive workpieces. In the HSEE process, the material removal takes place mainly due to the effect of thermal action but some electrochemical reaction occurs.
As to electrodes applied in electro-machining processes, especially for EDM and HSEE processes, electrical conductivity and thermal arc resistance are critical parameters. In some circumstances, electrodes with both high electrical conductivity and high thermal arc resistance may be required. Moreover, the electrodes may have specially tailored geometries, and possibly, need unique electrolyte flushing channels. The special tool geometries typically enable directed and uniquely tuned flushing in the cut zone. Flushing through the tool in this way improves chip evacuation thus reducing thermal damage at the part. A part with less thermal damage due to cutting will have longer life, a simplified manufacturing sequence, and a lower production cost. Therefore, making tools with specialized flushing manifolds that are complex build-ins and with tuned material properties like arc-resistance and electrical conductivity is highly desirable. However, there is no existing electrode which is able to meet the requirements using existing, conventional electrode fabrication methods like casting, milling, and turning. Often it is not possible to economically produce electrodes with both high electrical conductivity and high thermal arc resistance that additionally possess special geometries that enable unique flushing in the cutting zone.
Therefore, there is a need for both a new and improved electro-machining electrode with unique flushing geometries, material properties, and a method for fabricating the electrode.